Conventionally the radiation emitted by a radioactive source such as a particle of mineral ore is measured by a crystal detector which has a flat receptor surface adjacent to which the particle is placed or past which it is moved while being measured for radioactivity. A difficulty with this system of radiation measurement is that the radiation emissions from a particle are in all directions from the source of radiation in the particle with the radiation in the various directions being of varying intensities due to varying degrees of radiation absorption by the material of the irregularly shaped particle. With this above system of measurement, errors may and in fact do occur in practice by the particle being oriented towards the detector in the direction in which it is least radio emissive.
A further complication with the above measuring system is that the detector must measure the radio-active count of the particle against a background of natural cosmic and other radiation. This is a serious difficulty when measuring the radio-active count of ores, such as those mined in South African gold mines, which are poorly emissive as opposed to uranium ore and in fact have emission levels very close to the background count.